The Logos Historica Verita is a small Imperial organisation dedicated to recovering a full and accurate accounting of the history of Mankind unmarred by religious superstition or political bias. It was created by Roboute Guilliman, the Lord Commander of the Imperium and the Primarch of the Ultramarines Chapter, some time after his resurrection in 999.M41. It was the Primarch's intent to make a full and accurate accounting of the Imperium of Man's fragmentary and often contradictory history, the truth of which would inevitably help humanity's advancement out of the darkness that had befallen it in the millennia after the Horus Heresy. For this task, Guilliman utilised individuals of an inquisitive and more liberal nature, and after training them personally in objective methods of data collection, assigned them the daunting task of discovering, collating and cataloging thousands of standard years of human history that had been lost or was woefully inaccurate due to superstition, suppression or purposeful obfuscation by the High Lords of Terra.
Not long after the Primarch's resurrection and assumption of the mantle of the Lord Commander of the Imperium, Guilliman launched his Indomitus Crusade to push back the encroaching Forces of Chaos that had been unleashed across the galaxy after the birth of the Great Rift. When the demands of war retreated, the Primarch was not idle, for he worked tirelessly within his scriptorium aboard his flagship, the Macragge's Honour. Even after a standard century on from his rebirth in 999.M41, Guilliman had yet to grasp all the events of the last ten millennia since he fell at the Battle of Thessala to the Daemon Primarch Fulgrim. He was dismayed to find that much of Mankind's history, like so much else once based on objective reason, had fallen afoul of superstition, fanaticism and hearsay. If anything, the state of man's knowledge was now worse than it had been after the Unification Wars, when the Emperor had unified Terra before the Great Crusade. Much of Terra's ancient history, painstakingly pieced together by the Remembrancers of Guilliman's own era, had been lost again.
Knowledge of the Immaterium's true nature had been suppressed, but only intermittently, throughout Mankind's long and turbulent history. Even though it had become impossible to fully suppress the dire nature of the Warp, that had not stopped the Inquisition from trying, for knowledge of daemons or the Ruinous Powers was strictly forbidden to Imperial citizens. Many innocents had paid the ultimate price for accidentally learning the truth of such matters. Even Guilliman, the Imperial Regent himself, faced opposition from the Inquisition in his quest for knowledge. To oppose their puritanical redactionism, he had trained his own corps of historitors. Between campaigns, he sought out inquisitive minds, exactly the sort that had long been frowned upon within the Imperium, rescuing them from penal servitude and impending brain wipe. The first handful he had tutored himself, when time allowed. They in turn taught more, and more still. Each one was assessed by the Primarch personally. Those that passed were given the rank of Historitor-Investigatus. Those that failed to meet his exacting standards were given less taxing roles within the new organisation, as librarians, servants and assistants. From his reading of the histories available, Guilliman had learnt that the brutal machinery of Imperial government was unkind to failures, yet another thing that saddened him about the present age. The Primarch already had enough blood upon his conscience. No life in the Imperium henceforth was to be wasted.
As the century since his rebirth wound on, the numbers of historitors grew from four, to eight, to sixteen -- until by circa 100.M42, the Logos Historica Verita numbered five hundred operatives and a thousand support staff. Utilising long-dead academic arts, they attempted the impossible: the construction of a reliable history of the Imperium of Man. Against great odds, small cells of the Logos searched out ancient records. At their presentation of the Primarch's seal, forbidden vaults were opened and emptied, their contents copied and dispatched to Guilliman's Crusade wherever it was. The Logos' work was a torturous, dangerous affair. Warzones now engulfed half the galaxy in the early years of the 42nd Millennium, and his historitor teams sometimes disappeared into them without trace. Often, they were opposed by the existing powers that be, as well as the more conservative agents of the Inquisition. But Guilliman would not be stopped, his determination to restore humanity's truth irrepressible.
The task of compiling a full and accurate accounting of the history of humanity was a monumental and nigh-impossible task, compounded further by the fact that even the Imperial Dating System was woefully inaccurate. As the Primarch digested thousands of standard years of history recorded upon every device conceivably employed by mankind, he had come to learn of the Chronostrife of Terra, a bitter, ongoing internal war within the Ordo Chronos over the Imperium's dating system. What he read made him despair. Not even his father's calendar had survived the millennia intact. During the Great Crusade and the Horus Heresy, the standard dating system had provided some idea of the order of events over time, but like everything else the Emperor had created, the calendar had become degraded by both dogmatic adherence and thoughtless revisionism. Various rival dating systems had evolved from the Imperial Standard, making a true chronicle of the human-settled galaxy almost impossible to construct. As the Indomitus Crusade drew to a close around 111.M42, Guilliman calculated the current year by the five main factional variants of the Imperial Calendar to be anywhere between the early 41st Millennium and an entire millennium later, and that was leaving out the numerous lesser, more heretical interpretations. Guilliman had been hoping to find a solution to the Imperium's tortured dating system; he had instead found there was none. It was something else that would ultimately require his personal attention to repair.
- Dark Imperium (Novel) by Guy Haley, Ch. 9 "Imperator Gloriana," pp. 94-97